The use of radiation as a means for selectively destroying malignant cells has been known for some time. In cases where the malignancy is localized, there are a number of advantages to localizing the administration of radiation to the site of malignancy. One means of locally administering dosages of radioactivity is to implant radioactive material into the body so that it resides at the site of the malignancy. Such material may be provided in the form of microspheres or pellets containing a radioactive isotope. This method has the further advantage in that radiation is continuously administered to the tissue.
It is known, for example, to provide microspheres, such as glass microspheres, that contain a radioactive isotope within the glass. Radioactive glass microspheres having diameters between about 15 and 50 microns are particularly useful in the treatment of malignant liver tumors. The microspheres are introduced along with a body-compatible carrier fluid into the hepatic artery, whereupon the microspheres travel to and lodge in capillaries of the liver and in liver tumors. The liver receives approximately 20% of its blood supply through the hepatic artery and the remaining 80% from the portal vein which leads from the digestive organs. Liver tumors, on the other hand, tend to draw their entire blood supply from the hepatic artery; thus, radioactive microspheres introduced into the hepatic artery selectively localize in capillaries associated with liver tumors.
In the past, radioactive microspheres have been simply injected into the bloodstream via a catheter, usually with a syringe having an awkward shield to protect the physician from radiation. In addition to shielding problems, many insoluble radioactive materials are difficult to administer in controlled dosages. The radioactive isotopes that are generally incorporated in radioactive microspheres or pellets for localized radiation treatment have short half-lives. Thus, there is a very significant, though entirely predictable, loss of radioactivity (decay) from the time the material is shipped from the place of manufacture until it is administered to a patient. The amount of material to be administered, therefore, is a function of the amount of measured radioactivity per mass of material and of the time interval between the date of measurement and the date of administration.
Heretofore, insoluble radioactive material has been provided in vials along with a volume of carrier liquid. The radioactivity of the material is measured at a certain time, which is dated on the vial, and the physician is provided tables relating desired dosage to date of use. Immediately prior to usage, the vial is shaken until the insoluble material is, presumably, homogeneously distributed throughout the carrier liquid, and an appropriate volume is withdrawn by syringe.
Delivery of a desired dosage by syringe withdrawal measurement rests upon the assumption that the insoluble material is homogeneously distributed throughout the carrier fluid; however, this is a very dubious assumption, especially with denser materials. Even attempts to maintain agitation, e.g., by continuous stirring, while withdrawing the insoluble material and carrier liquid, may not assure a withdrawal of insoluble particles that is proportional to the volume withdrawn. Glass microspheres typically have a density of about 3.1 gm/cm.sup.3, whereas isotonic saline, or another suitable carrier salt solution, has a density only slightly greater than unity. Administration of a desired dosage of dense insoluble material based upon suspension volume is inherently unreliable.
Syringe injection introduces further uncertainties of dosage. For reasons, such as mechanical entrapment or electrostatic attraction of surfaces, a potentially significant portion of the insoluble radioactive material tends to remain in the syringe.
The need exists for systems and methods for delivering insoluble materials into an animal body, including a human body, with more precise control over dosage. Where the insoluble material is radioactive, the need exists for better shielding of the material from the physician.